(1) Field of Invention
This invention relates to centrifugal pumps for moving fluids or slurries of varying viscosities. In particular, it relates to such pumps having impellers which by laminar action or friction induced movement to the contained medium in the similar manner that movement of a fluid through a stationary pipe is restricted by the friction of the pipe.
(2) Description of the Prior Art
Most impellers for centrifugal pumps have some type of vane to impart movement to the contained fluid or slurry through the pump. These vane-type impellers have limited life because of the problem of cavitation which is the gradual deterioration or erosion of the surfaces of the vanes over time due to the movement of the materials in and around the vanes, creating pockets of vapor which explode causing damage. In addition, the typical vane-type impeller offers a very high starting torque under loaded conditions. Also, many pumps designed for the movement of high viscosity slurries are limited as to the particulate size that can be safely transited through the pump without unduly eroding the pump parts. Because of these problems, most pump parts must be manufactured of highly durable, and therefore expensive, materials. Also such pumps relatively high operating costs. The impeller of the instant invention has no such material two conoidal shells rectilinear generatrixes which may be convergent, divergent or curvilinear and connected by rectlinear or helical ribs. There were a number of attempts in later years to improve the efficiency of impellers. Denys, in 1946, designed a disc of concave-convex profile, a disc of uniform strength, in which the stress at any point between the center and the rim was constant. His operating principle was that lighter molecular weight gases impinge more frequently on the rotating disk from left to right. The tangential component of rotation propels heavier molecules towards the outer periphery from where they are scavenged; lighter gas molecules are scavenged from the central outlet. Later Grantham (1951) developed a centrifugal pump in which the impeller (frusto-conical) had a conical liquid-engaging surface with spiral grooves cut therein. Pumping space was adjustable to vary the volume of liquid pumped. A modification of the invention had a multi-cone impeller.
Perhaps the closest prior art to the present invention is found in the pumps of Kletschka et al. (1975) which were capable of use as heart pumps and blood pumps. Circular fluid rotators (accelerators) were outwardly convergent and rotated to impel the fluid circularly at substantially the speed of the rotators. Angular velocity of the rotator increased as the radial distance from the axis increased. The pumping action was radially increasing pressure gradient pumping or more specifically, it was constrained force-vortex radially increasing pressure gradient pumping. The rotators were of hollow frusto-conical form, convergent at the peripherals. These same inventors designed similar devices, apparently with the primary objective of developing apparatus for use with delicate fluids.
Less specific prior art is found in the "turbine" of Glass (1977) which is a multi-disk plate turbine reminiscent of Tesla. The turbine had tangential nozzle delivery to peripheral portions of the plates to impart motion. Discharge was through the center. Spiral like fencing was found between adjacent plates.
Recent tangential art known to these inventors is the patent of Hergt et al (1980) which pump was designed for reducing cavitation-induced erosion of centrifugal pumps. A conical or stepped intake diffuser directs flow of part-load eddy from impeller back into intake fluid pulse flow. Downstream portion of the diffuser constitutes an integral part of the impeller. The present invention is designed to overcome the drawbacks of prior art impellers that are subject to cavitation and to solve other problems associated with centrifugal pumps designed primarily for pumping slurries.
Prior art known to these inventors includes the following U.S. Pat. Nos.:
______________________________________ 651,400 6/1900 Trouve & Bellot 2,392,124 1/1946 Denys 2,569,563 10/1951 Grantham 2,977,042 3/1961 Jassniker 3,864,055 2/1975 Kletschka et al. 3,957,389 5/1976 Rafferty et al. 3,970,408 7/1976 Rafferty et al. 4,036,584 7/1977 Glass 4,037,984 7/1977 Rafferty et al. 4,239,453 12/1980 Hergt et al. ______________________________________